This invention relates to a method for the preparation of siloxane-containing bischloroformates. More particularly the method relates to a continuous method for the preparation of siloxane-containing bischloroformates in a flow reactor.
Silicone-containing copolycarbonates-are prized for their unique combination of ductility, toughness, and flame retardancy. Silicone copolycarbonates are typically prepared by reaction of a mixture of a siloxane-containing bisphenol and a bisphenol such as bisphenol A under interfacial conditions with phosgene and an aqueous acid acceptor such as sodium hydroxide in water. Alternatively, silicone copolycarbonates may be prepared by reaction of a chloroformate-terminated polycarbonate oligomer with a siloxane-containing bisphenol. Typically, the reaction between the chloroformate-terminated polycarbonate oligomer and the siloxane-containing bisphenol is carried out under interfacial conditions similar to those employed when a bisphenol and a siloxane-containing bisphenol are copolymerized directly with phosgene. Such approaches to silicone-containing copolycarbonates are illustrated in Japanese Patent Application JP 9265663, European Patent Application EP 500131, U.S. Pat. No. 5,530,083, U.S. Pat. No. 5,502,134, and copending U.S. patent application Ser. No. 09/613,040.
Siloxane-containing bischloroformates are potentially attractive chemical intermediates for the preparation of silicone-containing materials, including silicone-containing copolycarbonates in which the silicone-containing monomer is incorporated into the polymer as an electrophilic species. As such, improved methods for the preparation of siloxane-containing bischloroformates represent attractive goals. The present invention provides a simple, continuous, high yield method for the preparation of high purity siloxane-containing bischloroformates which is superior to known methods of bischloroformate preparation.